Hyundai Repair: Hyundai Santa Fe troubleshooting Code P0455, hyundai santa fe, emission control system

Question
I had the vehicle scanned and the code P0455(EVAP Emission Control System Leak--Large) come up.  We cleared the code, however, I checked to make sure the fuel cap was on correct and tight and it was.  The vehicle acts like it can not get gas and bogs down at times. Also, on several occasions the vehicle has almost stopped running. What does your experience say the problem is and the best way to get the problem fixed?

Answer
The diagnostic trouble code P0455 is typically unrelated to any performance issue.

The engine control module tests for fuel vapor leaks by selectively applying engine vacuum through the purge control valve and monitoring vacuum in the fuel tank while the valve that allows venting through the charcoal canister to the atmosphere (close valve) is closed.  P0455 sets if the engine is unable to pull the predetermined vacuum level on the fuel tank.

This could be caused by the fuel cap (which you've already checked) or any leak in the fuel vapor system.  If you're unable to visually see a broken hose or component which would cause a leak, the next step typically requires specialized equipment to check for leaks.  

This could also be caused by anything which would cause the vacuum to not reach the tank in the first place, such as a stuck closed purge valve or the vacuum line between the engine and purge valve being broken.


If the engine nearly stops running, I find it odd that there are no trouble codes related to the performace issue.  This type of problem could be caused by low fuel pressure.


Potentially, you could have a problem with a catalytic converter.  If the exhaust is restricted due to a converter coming apart, this could cause a insufficient engine vacuum to be applied to the fuel tank to reach the predetermined vacuum level, and it could cause the engine to run poorly, especially at higher throttle openings and higher rpms.


Unfortunately, there's no lone common cause for these issues, so I cannot advise you to make any repairs prior to definitively locating the issue.  I'd say to check what you can: fuel vapor lines, purge valve for being stuck open, and even the converter if you can take the exhaust apart to check whether the converter is coming apart.  Beyond that, it's probably cheaper to pay for professional diagnosis rather than guess at causes.